1. Field of the Invention
This invention relates to a printing apparatus.
2. Prior Art
There has been a demand for a printing apparatus capable of printing a large-sized or a large-volume image (including an image having a large number of dots due to high density of the image) at a higher speed. In the case of a printing apparatus whose print head is caused to scan a print medium for printing, a possible solution to an increased printing speed is to increase the scanning speed or increase a printable quantity per scan. The former has limits in accuracy of driving and braking control for scanning, and resulting accuracy of positioning control. On the other hand, the latter is capable of increasing the printable quantity per scan, in theory, by using a plurality of print heads (so-called multi-head).
For instance, as shown in FIG. 13, by using N print heads, PH(1), PH(2) where N is an integer equal to or lager than 2 (in the illustrated example, N=2), a larger number of lines of dots (hereinafter referred to as xe2x80x9cdot linesxe2x80x9d) can be printed per scan. In the illustrated example, the two print heads PH(1) and PH(2) each have M nozzles in the case of an ink jet type, or M thermal heads (heating elements) in the case of a thermal transfer type. In the following, the nozzles and thermal heads of the two types of print heads are generically referred to as nozzles. The print head PH(1) has 10 (=M) nozzles J11, J12, . . . , J19, and J1A, while the print head PH(2) has 10 (=M) nozzles J21 to J2A. That is, by using two (=N) print heads each of which can print 10 (=N) dot lines per scan, it is possible in theory to print 20 (Mxc3x97N) dot lines per scan.
However, in arranging the print heads PH(1) and PH(2) as shown in FIG. 12, the accuracy of the distance indicated by d in the figure causes a problem. It is possible to manufacture a print head such that the distance between the nozzle J11 and the nozzle J12, for instance, is equal to or shorter than 10 xcexcm, but it is practically impossible to arrange the print heads such that the distance d between the nozzle J1A at one end of the print head PH(1) and the nozzle J21 at an opposed end of the print head PH(2) is equal to or shorter than 10 xcexcm. Further, even if the arrangement may be possible, for the time being, a dimensional error occurs due to changes in temperatures of the print heads themselves. As a result, due to lowered accuracy of the inter-nozzle arrangement, a dot line L1A printed by the nozzle J1A and a dot line J21 printed by the nozzle J21 can appear to have a blank line between them differently from boundaries between other dot lines, causing a noticeably degraded print image quality. In short, due to a low inter-nozzle position accuracy, the print quality is degraded.
It is an object of the invention to provide a printing apparatus which is capable of increasing the printing speed by employing a multi-head structure and at the same time maintaining or enhancing print quality.
To attain the above object, the present invention provides a printing apparatus for printing on a print medium by using N print heads, where N is an integer equal to or larger than 2, assuming that two axes orthogonal to each other on a two-dimensional rectangular coordinate system are set to an X axis and a Y axis, each of the print heads being capable of printing M dots in a direction along the Y axis simultaneously, where M is an integer equal to or larger than 3, and at the same capable of printing M dot lines each extending in a direction along the X axis, by relative scan on the print medium in the direction along the X axis, the M dot lines being arranged side by side in the direction along the Y axis.
The printing apparatus according to the invention is characterized in that at least two print heads of the N print heads are arranged in a manner such that selected ones of the M dot lines that can be printed by one of the at least two print heads overlap selected ones of the M dot lines that can be printed by another of the at least two print heads.
According to this printing apparatus, there is employed a multi-head structure which uses N print heads each capable of printing M dots or M dot lines in a manner juxtaposed in a direction along the Y axis. Therefore, it is possible to increase the printing speed. Further, at least two print heads of the N print heads are arranged in a manner such that selected ones of the M dot lines that can be printed by one of the at least two print heads overlap selected ones of the M dot lines that can be printed by another of the at least two print heads. Therefore, it is possible to prevent degradation of print quality, caused e.g. by blank lines appearing between dot lines printed by the at least two print heads. That is, part of the dot lines which can cause the problem of degraded print quality can be printed by the at least two print heads in an overlapping manner, so that the print quality can be maintained or enhanced without demanding practically impossible positioning accuracy of the print heads. Therefore, it is possible to increase the printing speed by employing the multi-head structure, and at the same time maintain or enhance the print quality.
Preferably, the at least two print heads are arranged in a manner such that L dot lines of the M dot lines that can be printed by one of the at least two print heads overlap L dot lines of the M dot lines that can be printed by another of the at least two print heads, where L is a natural number satisfying the relationship of L less than M.
According to this preferred embodiment, the at least two print heads are arranged in a manner such that L dot lines of the M dot lines that can be printed by one of the at least two print heads overlap L dot lines of the M dot lines that can be printed by another of the at least two print heads, where L is a natural number satisfying the relationship of L less than M.
Therefore, dot lines to be printed by the at least two print heads are 2xc3x97Mxe2x88x92L dot lines and hence an increase in the printing speed is lowered by a degree corresponding to the L dot lines, i.e. the number of dot lines to be printed per scan is decreased thereby. However, it is possible to prevent degradation of print quality, caused e.g. by blank lines appearing between dot lines printed by the at least two print heads. That is, the L dot lines which cause the problem of degraded print quality can be printed by the at least two print heads in an overlapping manner, so that the print quality can be maintained or enhanced without demanding practically impossible positioning accuracy of the print heads. Therefore, it is possible to increase the printing speed by employing the multi-head structure, and at the same time maintain or enhance the print quality.
Alternatively, the at least two print heads are arranged in a manner such that L+2J dot lines of the M dot lines that can be printed by one of the at least two print heads overlap L+2J dot lines of the M dot lines that can be printed by another of the at least two print heads, where L is a natural number satisfying the relationship of Lxe2x89xa6Mxe2x88x922J, and J is a natural number satisfying the relationship of J less than M/2, and each of the at least two print heads is inhibited from printing J dot lines at a counterpart print head side end.
According to this preferred embodiment, the at least two print heads are arranged in a manner such that L+2J dot lines of the M dot lines that can be printed by one of the at least two print heads overlap L+2J dot lines of the M dot lines that can be printed by another of the at least two print heads, where L is a natural number satisfying the relationship of Lxe2x89xa6Mxe2x88x922J, and J is a natural number satisfying the relationship of J less than M/2. Therefore, if the dot lines are printed in this state, the L+2J dot lines can be printed in an overlapping manner. In this preferred embodiment, however, each of the at least two print heads is inhibited from printing J dot lines at an counterpart print head side end. This makes it possible to prevent degradation of print quality due to manufacturing errors of opposed ends of the print heads.
Alternatively, the at least two print heads are arranged in a manner such that L+J dot lines of the M dot lines that can be printed by one of the at least two print heads overlap L+J dot lines of the M dot lines that can be printed by another of the at least two print heads, where L is a natural number satisfying the relationship of Lxe2x89xa6Mxe2x88x92J, and J is a natural number satisfying the relationship of J less than M, and the one of the at least two N print heads is inhibited from printing J dot lines at a counterpart print head side end.
According to this print head, the at least two print heads are arranged in a manner such that L+J dot lines of the M dot lines that can be printed by one of the at least two print heads overlap L+J dot lines of the M dot lines that can be printed by another of the at least two print heads, where L is a natural number satisfying the relationship of Lxe2x89xa6Mxe2x88x92J, and J is a natural number satisfying the relationship of J less than M. Therefore, if the dot lines are printed in this state, the L+J dot lines can be printed in an overlapping manner. In this preferred embodiment, however, the one of the at least two N print heads is inhibited from printing J dot lines at an counterpart print head side end. This makes it possible to prevent degradation of print quality e.g. due to manufacturing errors of an end of the one of the print heads.
More preferably, the at least two print heads alternatively print each of dots of the L dot lines each extending along the X axis.
According to this preferred embodiment, the at least two print heads alternatively print each of dots of the L dot lines each extending along the X axis. Therefore, the L dot lines can be printed in an overlapping manner while causing each dot of the L dot lines to be alternatively printed by either of the at least two print heads.
Further preferably, the at least two print heads print the dots of the L dot lines in a predetermined order.
According to this preferred embodiment, the at least two print heads print the dots of the L dot lines in a predetermined order. Therefore, it is possible to print the dots of the L dot lines in an orderly overlapping manner.
Still more preferably, the at least two print heads alternately print each of the dots of the L dot lines.
According to this preferred embodiment, it is possible to print the L dot lines in an overlapping manner by causing the at least two print heads to alternately print each of the dots of the L dot lines, the dots being aligned in the direction along the X axis.
Still further preferably, the L is a plural number, and each of the at least two print heads print the dots of the L dot lines in a staggered arrangement.
According to this preferred embodiment, the L is a plural number, and by causing each of the two print heads to alternately print each of the dots of the L dot lines extending along the X axis, the dots of the L dot lines can be printed in an staggered arrangement to print the L dot lines in an overlapping manner.
Further preferably, the at least two print heads print the dots of the L dot lines in a random order.
According to this preferred embodiment, the at least two print heads print the dots of the L dot lines extending along the X axis in a random order. Therefore, it is possible to print the dots of the L dot lines in an overlapping manner such that the order of printing of each dot by either of the two print heads is random. This makes it possible to prevent the merging portion of respective sets of dot lines printed by the print heads from forming an orderly pattern, thereby further enhancing print quality.
Further preferably, the at least two print heads perform printing based on print data representing the M dot lines to be printed thereby, and each item of the print data based on which a corresponding one of the at least two print heads performs printing contains information concerning each dot as to whether the dot should be printed by the corresponding one of the at least two print heads.
According to this preferred embodiment, the at least two print heads print each perform printing based on print data representing the M dot lines to be printed thereby. In this case, each item of the print data based on which a corresponding one of the at least two print heads performs printing contains information concerning each dot as to whether the dot should be printed by the corresponding one of the print heads. Therefore, by simply performing printing according to the print data, it is possible to properly print the dots to be printed by the at least two print heads.
Still more preferably, the at least two print heads comprise a first print head and a second print head, and the printing apparatus further comprises allocation pattern-determining means for determining an allocation pattern which defines a manner of allocation of the dots of the L dot lines to the at least two print heads by a pattern, first print data-storing means for storing first print data representing M dot lines to be printed by the first print head, based on the allocation pattern, and second print data-storing means for storing second print data representing M dot lines to be printed by the second print head, based on the allocation pattern.
According to this print head, an allocation pattern is determined which defines a manner of allocation of the dots of the L dot lines to the at least two print heads by a pattern, and first print data representing M dot lines to be printed by the first print head and second print data M dot lines to be printed by the second print head are stored based on the allocation pattern. Therefore, the first print head and the second print head can print dots to be printed thereby simply by performing printing according to the first print data and the second print data, respectively.
Still further preferably, the first print data-storing means comprises pseudo first print data-storing means for storing pseudo first print data representing M dot lines to be printed by the first print head assuming the L dot lines to be printed by the first print head do not overlap the L dot lines to be printed by the second print head, first mask pattern-forming means for forming a first mask pattern indicative of part to be printed by the first print head based on the allocation pattern, and first print data-forming means for converting the pseudo first print data to the first print data by carrying out masking of data of the L dot lines out of the pseudo first print data based on the first mask pattern.
According to this preferred embodiment, pseudo first print data representing M dot lines to be printed by the first print head assuming that the L dot lines to be printed by the first print head do not overlap the L dot lines to be printed by the second print head is stored, and a first mask pattern indicative of part to be printed by the first print head is formed based on the allocation pattern. Then, the pseudo first print data is converted to the first print data by carrying out masking of data of the L dot lines out of the pseudo first print data based on the first mask pattern. That is, the pseudo first print data is converted to the first print data by using the first mask pattern based on the allocation pattern. Therefore, e.g. by once storing the pseudo first print data, and then performing data conversion after determining a print head to which each dot is to be allocated, it is possible to easily form the first print data. The second print data for the second print head can be similarly prepared.
Still further preferably, the first print data-storing means comprises first individual print data-storing means for storing first individual print data representing, out of the M dot lines to be printed by the first print head, Mxe2x88x92L dot lines which dot not overlap the L dot lines to be printed by the second print head, first common print data-storing means for storing first common print data representing, out of the M dot lines to be printed by the first print head, the L dot lines which overlap the L dot lines to be printed by the second print head, and the second print data-storing means comprises second individual print data-storing means for storing second individual print data representing, out of the M dot lines to be printed by the second print head, Mxe2x88x92L dot lines which dot not overlap the L dot lines to be printed by the first print head, second common print data-storing means for storing second common print data representing, out of the M dot lines to be printed by the second print head, the L dot lines which overlap the L dot lines to be printed by the first print head, the printing apparatus further comprising basic common print data-storing means for storing basic common print data representing the L dot lines in which the allocation of the dots of the L dot lines to the first print head and the second print head has not been reflected, and common print data-allocation means for allocating the basic common print data to the first common print data and the second common print data based on the allocation pattern.
According to this printing apparatus, there are stored first individual print data representing, out of the M dot lines to be printed by the first print head, Mxe2x88x92L dot lines which dot not overlap the L dot lines to be printed by the second print head, and first common print data representing, out of the M dot lines to be printed by the first print head, the L dot lines which overlap the L dot lines to be printed by the second print head, second individual print data representing, out of the M dot lines to be printed by the second print head, Mxe2x88x92L dot lines which dot not overlap the L dot lines to be printed by the first print head, and second common print data representing, out of the M dot lines to be printed by the second print head, the L dot lines which overlap the L dot lines to be printed by the first print head. In this case, basic common print data representing the L dot lines in which the allocation of the dots of the L dot lines to the first print head and the second print head has not been reflected is allocated to the first common print data and the second common print data based on the allocation pattern. Therefore, by adding the first individual print data and the second individual print data to the first common print data and the second common print data, respectively, it is possible to easily form the first print data and the second print data.
Preferably, the N print heads are each formed by an ink jet print head having at least M nozzles each for ejecting ink, the ink jet print head being capable of printing the M dots simultaneously by ink ejected from the M nozzles.
According to this preferred embodiment, the N print heads are each formed by an ink jet print head capable of printing M dots simultaneously by ink ejected from its M nozzles. Therefore, the present invention can be applied to a printing apparatus of ink jet type.
Preferably, the printing apparatus includes print image data-storing means for storing print image data representing a print image to be printed on the print medium, and the print image data contains binary data representing execution and inhibition of printing of each dot by binary expression.
According to this preferred embodiment, print image data representing a print image to be printed on the print medium is stored, and the print image data contains binary data representing execution and inhibition of printing of each dot by binary expression. Therefore, by allocating the print image data to the N print heads, each print head can easily print a portion to be printed thereby.
More preferably, the print image is a color image, and the print image data contains binary data representing each color of the color image.
According to this preferred embodiment, the print image is a color image, and the print image data contains binary data representing each color of the color image. Therefore, even though the print image is a color image, it is possible to cause each print head to print dots to be printed thereby, only by allocating the dots to the N print heads.
Preferably, the print medium is in a continuous form, and mounted in the printing apparatus such that a direction along length of the print medium coincides with the direction along the X axis.
According to this preferred embodiment, the print medium is in a continuous form, and mounted in the printing apparatus such that a direction along length of the print medium coincides with the direction along the X axis. Therefore, it is possible to increase an amount to be printed per scan, thereby further increasing the printing speed.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.